Crystal structures of aspartate semialdehyde dehydrogenases

Abstract

The present invention relates to novel drug targets for pathogenic bacteria. Accordingly, the invention provides purified protein comprising the amino acid sequence set forth in SEQ ID NO: 4. The invention also provides biochemical and biophysical characteristics of the polypeptides of the invention.

1 . A composition comprising an isolated, recombinant polypeptide, wherein the polypeptide comprises: (a) an amino acid sequence set forth in SEQ ID NO: 2 or SEQ ID NO: 4; (b) an amino acid sequence having at least about 95% identity with the amino acid sequence set forth in SEQ ID NO: 2 or SEQ ID NO: 4; or (c) an amino acid sequence encoded by a polynucleotide that hybridizes under stringent conditions to the complementary strand of a polynucleotide having SEQ ID NO: 1 or SEQ ID NO: 3 and has at least one biological activity of aspartate semialdehyde dehydrogenase from  P. aeruginosa ; and wherein the polypeptide of (a), (b) or (c) is at least about 90% pure in a sample of the composition.  
     
     
         2 . The composition of  claim 1 , wherein the polypeptide is at least about 95% pure as determined by gel electrophoresis.  
     
     
         3 . The composition of  claim 1 , wherein the polypeptide is purified to essential homogeneity.  
     
     
         4 . The composition of  claim 1 , wherein at least about two-thirds of the polypeptide in the sample is soluble.  
     
     
         5 . The composition of  claim 1 , wherein the polypeptide is fused to at least one heterologous polypeptide that increases the solubility or stability of the polypeptide.  
     
     
         6 . The composition of  claim 1 , which further comprises a matrix suitable for mass spectrometry.  
     
     
         7 . The composition of  claim 6 , wherein the matrix is a nicotinic acid derivative or a cinnamic acid derivative.  
     
     
         8 . A sample comprising an isolated, recombinant polypeptide, wherein the polypeptide comprises: (a) an amino acid sequence set forth in SEQ ID NO: 2 or SEQ ID NO: 4; (b) an amino acid sequence having at least about 95% identity with the amino acid sequence set forth in SEQ ID NO: 2 or SEQ ID NO: 4; or (c) an amino acid sequence encoded by a polynucleotide that hybridizes under stringent conditions to the complementary strand of a polynucleotide having SEQ ID NO: 1 or SEQ ID NO: 3 and has at least one biological activity of aspartate semialdehyde dehydrogenase from  P. aeruginosa ; and wherein the polypeptide of (a), (b) or (c) is labeled with a heavy atom.  
     
     
         9 . The sample of  claim 8 , wherein the heavy atom is one of the following: cobalt, selenium, krypton, bromine, strontium, molybdenum, ruthenium, rhodium, palladium, silver, cadmium, tin, iodine, xenon, barium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, mercury, thallium, lead, thorium and uranium.  
     
     
         10 . The sample of  claim 8 , wherein the polypeptide is labeled with seleno-methionine.  
     
     
         11 . The sample of  claim 8 , further comprising a cryo-protectant.  
     
     
         12 . The sample of  claim 11 , wherein the cryo-protectant is one of the following: methyl pentanediol, isopropanol, ethylene glycol, glycerol, formate, citrate, mineral oil and a low-molecular-weight polyethylene glycol.  
     
     
         13 . A crystallized, recombinant polypeptide comprising: (a) an amino acid sequence set forth in SEQ ID NO: 2 or SEQ ID NO: 4; (b) an amino acid sequence having at least about 95% identity with the amino acid sequence set forth in SEQ ID NO: 2 or SEQ ID NO: 4; or (c) an amino acid sequence encoded by a polynucleotide that hybridizes under stringent conditions to the complementary strand of a polynucleotide having SEQ ID NO: 1 or SEQ ID NO: 3 and has at least one biological activity of aspartate semialdehyde dehydrogenase from  P. aeruginosa ; wherein the polypeptide of (a), (b) or (c) is in crystal form.  
     
     
         14 . A crystallized complex comprising the crystallized, recombinant polypeptide of  claim 13  and a co-factor, wherein the complex is in crystal form.  
     
     
         15 . A crystallized complex comprising the crystallized, recombinant polypeptide of  claim 13  and a small organic molecule, wherein the complex is in crystal form.  
     
     
         16 . The crystallized, recombinant polypeptide of  claim 13 , which diffracts x-rays to a resolution of about 3.5 Å or better.  
     
     
         17 . The crystallized, recombinant polypeptide of  claim 13 , wherein the polypeptide comprises at least one heavy atom label.  
     
     
         18 . The crystallized, recombinant polypeptide of  claim 17 , wherein the polypeptide is labeled with seleno-methionine.  
     
     
         19 . A method for designing a modulator for the prevention or treatment of  P. aeruginosa  related disease or disorder, comprising: 
 (a) providing a three-dimensional structure for a crystallized, recombinant polypeptide of  claim 13;     (b) identifying a potential modulator for the prevention or treatment of  P. aeruginosa  related disease or disorder by reference to the three-dimensional structure;    (c) contacting a polypeptide of the composition of  claim 1  or  P. aeruginosa  with the potential modulator; and    (d) assaying the activity of the polypeptide or determining the viability of  P. aeruginosa  after contact with the modulator, wherein a change in the activity of the polypeptide or the viability of  P. aeruginosa  indicates that the modulator may be useful for prevention or treatment of a  P. aeruginosa  related disease or disorder.    
     
     
         20 . A sample comprising an isolated, recombinant polypeptide, wherein the polypeptide comprises: (a) an amino acid sequence set forth in SEQ ID NO: 2 or SEQ ID NO: 4; (b) an amino acid sequence having at least about 95% identity with the amino acid sequence set forth in SEQ ID NO: 2 or SEQ ID NO: 4; or (c) an amino acid sequence encoded by a polynucleotide that hybridizes under stringent conditions to the complementary strand of a polynucleotide having SEQ ID NO: 1 or SEQ ID NO: 3 and has at least one biological activity of aspartate semialdehyde dehydrogenase from  P. aeruginosa ; and wherein the polypeptide of (a), (b) or (c) is enriched in at least one NMR isotope.  
     
     
         21 . The sample of  claim 20 , wherein the NMR isotope is one of the following: 
 hydrogen-1 ( 1 H), hydrogen-2 ( 2 H), hydrogen-3 ( 3 H), phosphorous-31 ( 31 P), sodium-23 ( 23 Na), nitrogen-14 ( 14 N), nitrogen-15 ( 15 N), carbon-13 ( 13 C) and fluorine-19 ( 19 F).    
     
     
         22 . The sample of  claim 20 , further comprising a deuterium lock solvent.  
     
     
         23 . The sample of  claim 22 , wherein the deuterium lock solvent is one of the following: acetone (CD 3 COCD 3 ), chloroform (CDCl 3 ), dichloro methane (CD 2 Cl 2 ), methylnitrile (CD 3 CN), benzene (C 6 D 6 ), water (D 2 O), diethylether ((CD 3 CD 2 ) 2 O), dimethylether ((CD 3 ) 2 O), N,N-dimethylformamide ((CD 3 ) 2 NCDO), dimethyl sulfoxide (CD 3 SOCD 3 ), ethanol (CD 3 CD 2 OD), methanol (CD 3 OD), tetrahydrofuran (C 4 D 8 O), toluene (C 6 D 5 CD 3 ), pyridine (C 5 D 5 N) and cyclohexane (C 6 H 12 ).  
     
     
         24 . The sample of  claim 20 , which is contained within an NMR tube.  
     
     
         25 . A method for identifying small molecules that bind to a polypeptide of the composition of  claim 1 , comprising: 
 (a) generating a first NMR spectrum of an isotopically labeled polypeptide of the composition of  claim 1;     (b) exposing the polypeptide to one or more small molecules;    (c) generating a second NMR spectrum of the polypeptide which has been exposed to one or more small molecules; and    (d) comparing the first and second spectra to determine differences between the first and the second spectra, wherein the differences are indicative of one or more small molecules that have bound to the polypeptide.    
     
     
         26 . A host cell comprising a nucleic acid encoding a polypeptide comprising: (a) an amino acid sequence set forth in SEQ ID NO: 2 or SEQ ID NO: 4; (b) an amino acid sequence having at least about 95% identity with the amino acid sequence set forth in SEQ ID NO: 2 or SEQ ID NO: 4; or (c) an amino acid sequence encoded by a polynucleotide that hybridizes under stringent conditions to the complementary strand of a polynucleotide having SEQ ID NO: 1 or SEQ ID NO: 3 and has at least one biological activity of aspartate semialdehyde dehydrogenase from  P. aeruginosa ; wherein a culture of the host cell produces at least about 1 mg of the polypeptide per liter of culture and the polypeptide is at least about one-third soluble as measured by gel electrophoresis.  
     
     
         27 . An isolated, recombinant polypeptide, comprising: (a) an amino acid sequence having at least about 90% identity with the amino acid sequence set forth in SEQ ID NO: 4; or (b) an amino acid sequence encoded by a polynucleotide that hybridizes under stringent conditions to the complementary strand of a polynucleotide having SEQ ID NO: 1 or SEQ ID NO: 3 and has at least one biological activity of aspartate semialdehyde dehydrogenase from  P. aeruginosa ; and wherein the polypeptide comprises one or more of the following amino acid residues at the specified position of the polypeptide: Arg10, Thr36, Thr37, Ser38, Gln73, Val13, Gly168, Met12, Ala169, Asn39, Gly75, Arg102, Cys135, Lys244, Gln350, Ser165, or Gly166.  
     
     
         28 . A method for obtaining structural information of a crystallized polypeptide, the method comprising: 
 (a) crystallizing a recombinant polypeptide, wherein the polypeptide comprises: (1) an amino acid sequence set forth in SEQ ID NO: 2 or SEQ ID NO: 4; (2) an amino acid sequence having at least about 95% identity with the amino acid sequence set forth in SEQ ID NO: 2 or SEQ ID NO: 4; or (3) an amino acid sequence encoded by a polynucleotide that hybridizes under stringent conditions to the complementary strand of a polynucleotide having SEQ ID NO: 1 or SEQ ID NO: 3 and has at least one biological activity of aspartate semialdehyde dehydrogenase from  P. aeruginosa ; and wherein the crystallized polypeptide is capable of diffracting X-rays to a resolution of 3.5 Å or better; and    (b) analyzing the crystallized polypeptide by X-ray diffraction to determine the three-dimensional structure of at least a portion of the crystallized polypeptide.    
     
     
         29 . The method of  claim 28 , wherein the three-dimensional structure of the portion of the crystallized polypeptide is determined to a resolution of 3.5 Å or better.  
     
     
         30 . A method for identifying a druggable region of a polypeptide, the method comprising: 
 (a) obtaining crystals of a polypeptide comprising (1) an amino acid sequence set forth in SEQ ID NO: 2 or SEQ ID NO: 4; (2) an amino acid sequence having at least about 95% identity with the amino acid sequence set forth in SEQ ID NO: 2 or SEQ ID NO: 4; or (3) an amino acid sequence encoded by a polynucleotide that hybridizes under stringent conditions to the complementary strand of a polynucleotide having SEQ ID NO: 1 or SEQ ID NO: 3 and has at least one biological activity of aspartate semialdehyde dehydrogenase from  P. aeruginosa , such that the three dimensional structure of the crystallized polypeptide may be determined to a resolution of 3.5 Å or better;    (b) determining the three dimensional structure of the crystallized polypeptide using X-ray diffraction; and    (c) identifying a druggable region of the crystallized polypeptide based on the three-dimensional structure of the crystallized polypeptide.    
     
     
         31 . The method of  claim 30 , wherein the druggable region is an active site.  
     
     
         32 . The method of  claim 31 , wherein the druggable region is on the surface of the polypeptide.  
     
     
         33 . Crystalline aspartate semialdehyde dehydrogenase from  P. aeruginosa  comprising a tetragonal crystal having unit cell dimensions of a=b=168.810 Å, c=66.975 Å, α=β=γ=90° and space group P4 1 .  
     
     
         34 . A crystallized polypeptide comprising (1) an amino acid sequence set forth in SEQ ID NO: 2 or SEQ ID NO: 4; (2) an amino acid sequence having at least about 95% identity with the amino acid sequence set forth in SEQ ID NO: 2 or SEQ ID NO: 4; or (3) an amino acid sequence encoded by a polynucleotide that hybridizes under stringent conditions to the complementary strand of a polynucleotide having SEQ ID NO: 1 or SEQ ID NO: 3 and has at least one biological activity of aspartate semialdehyde dehydrogenase from  P. aeruginosa ; wherein the crystal has a P4 1  space group.  
     
     
         35 . A crystallized polypeptide comprising a structure of a polypeptide that is defined by a substantial portion of the atomic coordinates set forth in  FIG. 11 .